Asthma and other respiratory diseases have long been treated by the inhalation of appropriate medicament. For many years the two most widely used and convenient choices of treatment have been the inhalation of medicament from a drug solution or suspension in a metered dose pressurized inhaler (MDI), or inhalation of powdered drug generally admixed with an excipient, from a dry powder inhaler (DPI).
Inhalation medicament therapy is the treatment of choice for most patients with air flow obstruction. Since the inhaled dose is typically small, side-effects are few and the onset of medicament action is rapid. However, unlike most forms of medicament therapy, the success of aerosol therapy requires that the patient master relatively complex techniques in order to consistently inhale the medicament effectively into the lung.
Even with good technique, it has been estimated that only a small proportion, e.g., 8-10%, of the administered dose will reach the lung, since approximately 80% of the dose will impact ineffectually on the oropharynx and 10% will escape. See, e.g., D. Smith, Practitioner, 232:507, 510 (1988). Consequently, efficacy is dependent on proper inhalation technique and proper use of the medicament delivery device.
Numerous studies have documented problems associated with the correct use of metered dose inhalation (MDI) devices. One common difficulty involves a "hand-lung" dysfunction problem, which amounts to an inability on the part of the patient using the device to coordinate actuation of the device at the proper time during inhalation. It has been estimated that many, if not a majority, of patients improperly use their devices on occasion, and therefore can receive an inadequate dose of medication.
The optimal sequences of patient maneuvers for the proper use of devices are known. However, ensuring patient compliance with such maneuvers has proven to be a significant problem. It has been shown that training can improve patient performance, as well as pulmonary function, as a result of better delivery of medicament to the airways. It has also been demonstrated that young children and the very elderly can also be trained to correctly use devices. Inevitably however, repeated training is needed to ensure compliance in the use of such devices.
A number of systems and approaches have been described for training in the use of inhalation devices. See, e.g., Coady et al., Practitioner, 217:273-275 (1976), Newman et al., J. Royal Soc. Med., 73:776-779 (1980), Shim et al., Am. J. Med., 69:891-894 (1980), Barron, Today's Therapeutic Trends, 6(2):13-17 (1988), and McElnay et al., J. Clin. Pharm. Therap., 14:135-144 (1989).
U.S. Pat. No. 4,984,158 (Hillsman) describes a metered dose inhaler biofeedback training and evaluation system that involves a visual and auditory biofeedback system that displays certain respiratory parameters along with real time performance or optimal performance. The system however is based on such parameters as (1) the integration of measured inspiration and expiration airflow in order to provide signals based on volume, and (2) the determination of a cyclic expiration point representative of lung exhaustion.
In terms of systems presently available, Vitalograph (Lenexa, Kans.) markets a product called "A.I.M." (Aerosol Inhalation Monitor), which is described as an incentive device using cartoon-like characters for training patients. The feedback to the patient involves a meter and a series of lights that signal correct or incorrect use of the MDI.
Vitalograph also markets "MDI-Compact" which combines an electronic spirometer with inhalation monitoring, and employs a visual screen.
It is apparent that inhalation medicament delivery devices can only achieve their full potential benefit to the patient if the patient is able to produce a near optimum inhalation maneuver on a regular basis. Consequently, it would be desirable to be able to improve the ability of a patient to practice using such a device, without actual drug delivery but with an indication of the acceptability of his or her performance.
It would be particularly desirable, in terms of more closely achieving true biofeedback, to have the option of having certain parameters of the patient's performance be evaluated in comparison to values that are specific to that patient, rather than by comparison to values that are somehow predetermined for the patient (e.g., either by a trainer/operator, or in the construction of the system itself).